|Speaker||Talk Date||Talk Series|
|Steve Balbus (Oxford)||6 February 2014||Institute of Astronomy Colloquia|
There is evidence that the saturation levels of MHD turbulence are
sensitive to the ratio of the small scale viscosity to resistivity,
a quantity known as the magnetic Prandtl number Pm. This sensitivity is present when Pm ~ 1.
Interestingly, discs associated with compact X-ray sources have such a low-to-high (tracking inward) Pm transition radius on scales of tens of Schwarzschild radii. These disc sources are also known for their dramatic changes in their spectral states.
In this talk, I will show that standard alpha disc theory predicts Dwarf-Nova like outbursts when the turbulent stress is even a modestly increasing function of Pm. Implications for understanding the X-ray data will be presented, both successes of the theory and remaining challenges.